JS controls the length of strings in the input box

// Get the byte length of the string
function len(s) {
s = String(s);
return + ((/[^\x00-\xff]/g) || "").length;// Add the matching full-width character length
}

function limit(obj, limit) {
var val = ;
if (len(val) > limit) {
val=(0,limit);
while (len(val) > limit){
val = (0, - 1);
};
= val;
}
}

$("#nickName").keyup(function(){
limit(this,20);//within 20 bytes
})